Container



Oct. 15,V 1946. T, s, CARSWELL 2,409,252

CONTAINER Filed Nov.4 7`, 1941v ATTORNEY `such as gasoline,` of the container.

Patented Oct. 15, 1946 CONTAINER Thomas S. CarswelLLongmeadow, Mass., assigner to Monsanto Chemical Company, St. Louis, Mo., va corporation of Delaware Application November 7, 1941, Serial No. 418,231

2 Claims. (Cl. 154-435) 'novel inner liner in combination with Walls having a self-sealing structure capable of sealing a hole made therein as by such a projectile as a bullet, and more particularly pertains to a selfsealing gasoline tank, especially suitable for a military airplane, having a novel inner liner in combination with the self-sealing means.

The construction of such 'a tank as one suitable for a military airplane, for example, which Will be not only self-sealing when punctured or .traversed as by such a projectile as a bullet but also otherwise satisfactory as a tank for such motor fuel as gasoline has long presented a very difficult problem. When a high velocity bullet passes through a tank containing a liquid such as gasoline, a pressure wave is set up in the liquid as the bullet passes through it creating a liquid hammer or ram effect against the opposite wall of the tank from Which the bullet entered. The result of this is a tendency to tear out a large hole where the bullet leaves the tank. This creates a special problem in constructing a self-sealing tank subject to being traversed or Ipunctured by a bullet, since, in addition to overcoming the tendency described above, such a tank must also be otherwise satisfactory for the purpose intended.

The kind of a container to which this invention particularly relates is a self-sealing gasoline tank, Which may, for example, have Walls comprising, from the outside toward the inside, a layer of very heavy hide leather, a layer of latex approximately 11s inch thick, a layer of sponge rubber about 1A; inch thick, another layer of latex about 11e inch thick, a layer of split hide, and an inner liner Which is contacted by the gasoline. The inner liner serves to retain or hold the gasoline, and the other layers serve as a support and as a self-sealing means when the Wallis traversed by a bullet. When a bullet passes through such a Wall properly constructed in accordance with this invention, it appears that the sponge rubber .tends to push into the hole to prevent substantial leakage of the gasoline, While thev latex swells,

when contacted by the gasoline, and expands to effect a sealing of the hole. The leather and hide impart strength and some rigidity .to the tank wall.

The requirements for a satisfactory inner liner for such a container are numerous and exacting. Such a liner must not only cooperate With the self-,sealing means in its function but also must serve as a satisfactory retainer for the contents, Among the 2 chief disadvantages of prior art materials-used for inner liners of containers of the kindreferred .to above are that such material was sub- J'ect to corrosion, or was deteriorated by the substances such as gasoline placed in the container, that the material would allow gasoline to be diffused therethrough .to the outer layers ofthe tank Wall at an'undesirably high rate, that the material Would permit extraction of substances by the contents of the container which would contaminate the contents rendering them unsuitable for the purpose intended (gasoline, for example, might be contaminated so as to be harmful to the motor when used as motor fuel) that When traversed by a bullet the liner would be shattered, thus exposing the outer layers of the tank Walls to the contents of the tank, or that the material of the liner after being traversed by the bullet, especially from the inside toward the outside accompanied by the liquid hammer or ram effect, would be expanded or torn out in such a Way as to hold open the hole left by the bullet by expanded protruded portions extending into the hole so that the self-sealing means could not function properly. Although one kind of a material might be more or less satisfactory'so far as many of the requirements are concerned, it would nevertheless have suicient disadvantage to render the container highly unsatisfactory in some particular respect. For example, even though a thin sheet of aluminum might be more or less satisfactory so far as many of the requirements are concerned, it has the outstanding disadvantage that the liquid ram effect, referred to above, usually leaves a large hole torn in the sheet with portions protruding into the hole Apreventing the functioning of the self-sealing means. Moreover, other materials, for example, numerous synthetic materials, even though satisfactory to some extent with regard .to one or some of the requirements, are unsatisfactory as to other important factors.

It is an object of this invention to provide a self-sealing container which avoids the foregoing disadvantages.

It is a'further object of .this invention to pron vide a selfsealing container having a novel inner liner in combination with the outer wall structure including the self-sealing means which improves thev container.

Another object of this invention is to provide an improved self-sealing motor fuel tank especially suitable for military airplanes subject to puncture by such a projectile as a bullet. 7 s,

Further and important objectsA of this inven- Letters Patent to Morrison et al., Reissue No.l

20,430, issued June 29, 1937, and in French Patent No. 793,175 exemplify resins suitable for the purpose of this invention.

These resinous compositions are tough,.elastic and flexible, and an inner liner made in accordance with this invention cooperates with the rest of the wall structure, including the self-sealing means, to produce remarkably improved results in a self-sealing container, especially a gasoline tank for a militaryairplane, for example.

The liners made in accordance with this invention do not corrode, as rnetals,` for example, are resistant toY deterioration byrwater or such contents as hydrocarbons including gasoline, benzene, lubricating oils, etc., have a surprisingly low average rate of diffusion therethrough by .suchmaterials as gasoline, do not permit extraction of substances by hydrocarbons which would contaminate the contents of the container,

Yespecially such hydrocarbons as gasoline, ben-A zene, lubricating oil, for example, are tough, elastic and flexible and cooperate with the outer wall layers, which include the self-sealing means, to

`make it possible to make a wall such that, even tank constructed .in accorda-nce with this invention, and Fig. 2 shows the layers ofthe wall structure in detail.

Atank is shown generallyA at I and thewall thereof at 2. Referring more particularly to Fig.

y2, the outer layer of the wall is shown at 3 and this may comprise a. tough wear-resistant material such as a rubber impregnated rayon, for example. Layers and 8 comprise amaterial which swells and expands when contacted by the contents of the container to eliect a sealing of a hole left as by a projectile, and for such hydrocarbons as gasoline, benzene and lubricating oils, for example, especially gasoline, a materialV such as latex is satisfactory. At is a layer of-such a material as vulcanized rubber which adds velasticity to the wall structure as a whole, and ap-4 pears to cushion the shock of a big-h speed pro jectile. The inner lining is shown at 'lV and comprises a polyvinyl acetal resin in accordance with this invention.

It is to be understood that 'other outer layers of wall structure may be used in combination with the novel inner liner o-f this invention, but that for a self-sealing container it is highly desirable that such outer layers include an element effectiveto seal arhole made by a-projectile and 'that the outerlayers besuch/ that the'wallstrucample; are especially suitable. 40.

4. ture as a whole is sufficiently strong, elastic and non-tearing that a projectile passing therethrough leaves a hole having a sufficiently small opening that `the sealing means can function properly. v

The inner liner 1 comprising the polyvinyl acetal is preferably in the form of a relatively thin sheet of such a resin. It may, however, with some advantage comprise a coating of such a resin applied to the inner surface of the outer layers, and, moreover, may be made by coating 4orimpregnating such a supporting material as duck, plywood or veneer, or by laminating a thin film of the resin to such a supporting material. As'pointed' out above, however, a thin sheet of the vresinous -niaterial is preferred, since this makes it possible to obtain greater advantages from this material in accordance with this invention.

The polyvinyl acetals for use in accordance with this invention may be made by the polymerization of vinyl -acetate or othervinyl'esters, followed by saponication Aand reaction with an aldehyde. These esters maybe polymerized to various degrees andunder different conditions before hydrolysis and reaction with the aldehyde. Moreover, the resultingacetals may -contain different proportions of ester, hydroxyl and acetal groups corresponding to the degree of hydrolysis and acetalization of the polymerized ester. It is desirable to select those polyvinyl acetal resins which a-re least affected or substantially unaffected by the contents of the container; for ex ample, for a' gasoline tank, itis desirable to use f those polyvinylV acetal resins which are gasoline insoluble orthe least'aifected by gasoline.

Polyvinylformaldehyde acetals, such as disclosed in the patents referredy to above, for ex- Usually the polyvinyl formals will be 'made by polymerizing the vinylY ester to Isuch a degree that a one-molar solution of the polymer in benzene lha'saviscosity of f from about 10 to 100 centipoises at '20 C., vhydrolyzing and'reacting such polymer with formaldehyde to produce a vpolyvinyl* formal resin having from substantially none to about 33 per cent acetate calculatedI as polyvinyl acetate and from about 5 to about 15 per cent hydroxyl calculated as polyvinyl alcohol, by weightyand the rest substantially acetal. In general it is desirable to'use a resin having a hydroxyl content ,greaterthan 'about 5 per centv and an'acetate content less thanV about 15 per cent. Thus, such a polyvinyl formal resulting from the polymerization of vinyl acetate' and hydrolysis and reaction of the polyvinyl acetate with formaldehyde to lform a polyvinyl formaldehyde acetal resin containing substantially 4 to 10% hydroxyl groups calculated as polyvinyl alcohol, 9.5 to 13% acetate by weight, calcula-ted as polyvinyl acetate, and the rest Substantially acetal, is-an example of a Apolyvinyl acetal suitable for --the present invention.

`cause of the :high Vresistance to such'hydrocarbons'as gasoline'or benzene, such as, for example, a polyvinyl formal having 14.6% .hydroxylcalculateclfas polyvinylvalcohol and 1.5% acetate,

and a polyvinyl formal having a 13.4% hydroxyl content and a 8.7% acetate content.

As another example, a polyvinyl acetal suitable for this invention results from the polymerization of vinyl acetate to such a degree that a onemolar solution of the polymer in benzene had a viscosity of substantially 25 centipoises at 20 C., and the hydrolysis and reaction of the polyvinyl acetate With butyraldehyde to form a polyvinyl acetal resin containing substantially 17 to 21 per cent hydroxyl groups calculated as polyvinyl alcohol, 3% or less acetate by weight and the rest acetal.

Moreover, this invention comprehends the use of other aldehydes, such as acetaldehyde, or mixtures thereof, or even ketones in making suitable polyvinyl acetals to be used in accordance with this invention. Thus, for example, acetaldehyde, propionaldehyde, Valeraldehyde, and hexaldehyde may be used. In general it is desirable to use a resin which will not be deteriorated to any substantial extent by the contents of the container, and in the case of such a hydrocarbon as gasoline or benzene, an acetal made With such lower aldehydes as formaldehyde or butyraldehyde is preferred.

The lm or sheet of polyvinyl acetal for this invention may be made by any of the known methods of forming such a resin into a lm or sheet, which should, of course, be non-porous for a fluid container. The resin may be extruded by means of suitable apparatus to produce a sheet, or a solution of the resin in a suitable solvent rnay be cast in any well-known manner and a film or sheet formed by evaporation of the solvent. Sheets of any desired thickness may be formed by these methods and a thickness of about .025 inch is usually suitable.

In general, depending on such factors as the use Which is to be made of the container, for eX- ample, other resinous materials such as cellulose acetate, cellulose triacetate, the copolymer of styrene with butadiene, ethyl cellulose and other cellulose esters may be used instead of the polyvinyl acetal resins as disclosed above.

The resinous materials used for the purpose of this invention may be plasticized, if desired, and in general most of the usual plasticizers may be used. For the polyvinyl acetal resins, and especially the polyvinyl formal resins, this invention comprehends the use of such plasticizers as, for example, diethyl phthalate, diacetin, dimethyl phthalate, dimethoxy ethyl phthalate, ethyl ethoxy ethyl phthalate, triacetin, methyl orl ethyl phthalyl ethyl glycollate, triethylene glycol dibutyrate, diethylene glycol dipropionate, triethylene glycol dihexoate, dibutyl and dimethyl sebacate, triethylene glycol esters of cocoanut oil acids, and others.

What I claim is:

l. In a gasoline container characterized by the ability to self-seal when in contact with gasoline after the passage of a bullet therethrough, a wall having a layer of rubber-impregnated rayon, a layer of latex, a layer of vulcanized rubber, another layer of latex and an inner layer comprising a plasticized sheet of polyvinyl formal resin containing by Weight from about 5 to 15% hydroxyl groups calculated as polyvinyl alcohol and from about 0 to 15% acetate groups calculated as polyvinyl acetate andthe rest substantially acetal.

2. In a gasoline container characterized by the ability to self-seal when in contact with gasoline after the passage of a bullet therethrough, a Wall having a layer of rubber-impregnated rayon, a layer of latex, a layer of vulcanized rubber, another layer of latex and an inner layer comprising a plasticized sheet of polyvinyl formal resin containing by weight from about 4 to 10% hydroXyl groups calculated as polyvinyl alcohol and from about 9:5 to 13% acetate groups calculated as polyvinyl acetate and the balance substantially acetal.

THOMAS S. CARSWELL. 

